Question 1107789: Jane took 30 min to drive her boat upstream to water-ski at her favorite spot. Coming back later in the day, at the same boat speed, took her 15 min. If the current in that part of the river is 6 km per hr, what was her boat speed in still water?
Answer by mananth(16946)   (Show Source):
You can put this solution on YOUR website! Jane took 30 min to drive her boat upstream to water-ski at her favorite spot. Coming back later in the day, at the same boat speed, took her 15 min. If the current in that part of the river is 6 km per hr, what was her boat speed in still water?
Let boat speed in still water be x
current speed = 6km/h
Let distance be y km
upstream speed = (x-6) km/h.
downstream speed = (x+6) km/h
time = distance / speed
y/(x-6) =1/2 hour
2y= x-6.............1
y/(x+6) = 1/4 hour
4y = x+6...............2
multiply equation (1) by 2
we get
4y= 2x-12...............3
therefore equation (2) = (3)
x+6 = 2x-12
2x-x = 18
x= 18
Speed of boat in still water is 18kmh
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